Motor having spoked outer rotor with spaced apart pole segments

ABSTRACT

An electric motor is provided. The electric motor comprises a stator and a rotor rotatable about an axis and spaced at least in part radially outside the stator. The rotor includes a plurality of arcuately spaced apart pole segments, a plurality of arcuately spaced apart magnets alternately arranged with the pole segments such that each of the pole segments is positioned between an adjacent pair of the magnets, a rotor can at least in part supporting the pole segments and the magnets, and a plurality of pegs. Each of the pole segments defines an opening therethrough and includes a generally arcuately extending wall structure positioned radially outside of and at least in part defining the opening. Each of the pegs extends through a corresponding one of the openings to secure a corresponding one of the pole segments relative to the can.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority from U.S. ProvisionalApplication No. 61/656,325, filed Jun. 6, 2012, and U.S. ProvisionalApplication No. 61/691,155, filed Aug. 20, 2012, the entire disclosuresof both of which are hereby incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to electric motors comprising arotor and a stator. More particularly, the present invention concernsouter rotor motors, wherein the rotor is of a spoked design and includesspaced apart pole segments.

2. Discussion of the Prior Art

Those of ordinary skill in the art will appreciate that electric motorsare often used in machines such as vertical- or horizontal-axis washingmachines, electric bicycles, and electric scooters. Fan, generators, andexercise equipment may also use electric motors. In many circumstances,design constraints include both performance requirements and spacerequirements.

SUMMARY

According to one aspect of the present invention, an electric motor isprovided. The electric motor comprises a stator and a rotor rotatableabout an axis and spaced at least in part radially outside the stator.The rotor includes a plurality of arcuately spaced apart pole segments,a plurality of arcuately spaced apart magnets alternately arranged withthe pole segments such that each of the pole segments is positionedbetween an adjacent pair of the magnets, a rotor can at least in partsupporting the pole segments and the magnets, and a plurality of pegs.Each of the pole segments defines an opening therethrough and includes agenerally arcuately extending wall structure positioned radially outsideof and at least in part defining the opening. Each of the pegs extendsthrough a corresponding one of the openings to secure a correspondingone of the pole segments relative to the can.

This summary is provided to introduce a selection of concepts in asimplified form. These concepts are further described below in thedetailed description of the preferred embodiments. This summary is notintended to identify key features or essential features of the claimedsubject matter, nor is it intended to be used to limit the scope of theclaimed subject matter.

Various other aspects and advantages of the present invention will beapparent from the following detailed description of the preferredembodiments and the accompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

Preferred embodiments of the invention are described in detail belowwith regard to the attached drawing figures, wherein:

FIG. 1 is a partial sectional bottom perspective view of a portion of amachine constructed in accordance with the principles of a preferredembodiment of the present invention, depicting a portion of a washingmachine and an outer rotor electric motor that includes, among otherthings, a rotor and a stator;

FIG. 2 is a bottom perspective view of a portion of the rotor of FIG. 1;

FIG. 3 is a top perspective view of the rotor portion of FIG. 2;

FIG. 4 is a partially sectioned view of the rotor portion of FIGS. 2 and3, particularly illustrating the means of spacing and securing the polesegments and magnets;

FIG. 5 is a partially sectioned view of a part of the rotor portion ofFIGS. 2 and 3, particularly illustrating the spacing and arrangement ofthe pole segments;

FIG. 6 is a partially sectioned view of a part of the rotor portion ofFIGS. 2 and 3, particularly illustrating the spacing and arrangement ofthe magnets;

FIG. 7 is a partially sectioned top view of a part of the rotor portionof FIGS. 2 and 3, particularly illustrating the relative dimensions andspacing of the pole segments and magnets;

FIG. 8 is a bottom perspective view of a portion of a rotor inaccordance with a second preferred embodiment of the present invention;

FIG. 9 is a top perspective view of the rotor portion of FIG. 8;

FIG. 10 is a partially sectioned view of the rotor portion of FIGS. 8and 9, particularly illustrating the means of spacing and securing thepole segments and magnets;

FIG. 11 is a partially sectioned, exploded view of a part of the rotorportion of FIGS. 8 and 9, particularly illustrating the spacing andarrangement of the pole segments and magnets and the means of securingthe pole segments and magnets; and

FIG. 12 is a partially sectioned top view of a part of a rotor inaccordance with a third preferred embodiment of the present invention,particularly illustrating keyhole openings in the pole segments.

The drawing figures do not limit the present invention to the specificembodiments disclosed and described herein. The drawings are notnecessarily to scale, emphasis instead being placed upon clearlyillustrating the principles of the preferred embodiments.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is susceptible of embodiment in many differentforms. While the drawings illustrate, and the specification describes,certain preferred embodiments of the invention, it is to be understoodthat such disclosure is by way of example only. There is no intent tolimit the principles of the present invention to the particulardisclosed embodiments.

With initial reference to FIG. 1, an electric motor 10 constructed inaccordance with a first preferred embodiment of the present invention isdepicted for use in a machine 12. Although a variety of machines aresuitable, as noted above, the particular machine depicted in FIG. 1 is awashing mashing having a stationary tub 14 and a rotatable washer oragitator basket (not shown).

As is customary, the motor 10 broadly includes a rotor 16 and a stator18 (shown schematically) spaced partially inside the rotor 16 so that acircumferentially extending gap 20 is defined between the rotor 16 andthe stator 18. Preferably, the rotor 16 is rotationally supported on thetub 14 by a bearing assembly 22. In the preferred embodiment shown inFIG. 1, the bearing assembly 22 includes a plurality of ball bearings 24disposed between an inner race 26 and an outer race 28, although adifferent bearing type or an entirely different rotation isolationmechanism could be used to similar effect without departing from thespirit of the present invention.

The stator 18, though shown only schematically in FIG. 1, preferablycomprises a core and a plurality of coils wound around the core. Thecore preferably comprises a plurality of arcuately spaced apart,radially extending teeth. The core may be arcuately or circumferentiallycontinuous or discontinuous. The teeth are preferably of a laminateddesign, although it is with the scope of the present invention forintegrally formed teeth to be provided. A wide variety of tooth shapesfall within the scope of the invention.

The coils preferably comprise electrically conductive wiring. The wiringpreferably comprises aluminum wiring, although copper or anotherelectrically conductive material could also be used without departingfrom the scope of the present invention. In the preferred embodiment,the stator core is at least partly coated with an electricallyinsulative coating, preferably a powder coating. One suitable powdercoating material is available from 3M™ under the designation Scotchcast™Electrical Resin 5555. However, it is within the scope of the presentinvention for the stator core to be insulated with other electricallyinsulative coatings or use other insulation arrangements such aselectrically non-conductive tabs or overlays.

Preferably, mounting structure (not shown) is provided to fix the stator18 to the machine 12 and to support it thereon. In the first illustratedembodiment, the stator 18 is mounted onto the machine 12 via fixation toa tub mounting hub 30. The stator may be mounted in any suitable manner,including those manners disclosed in U.S. patent application Ser. Nos.13/312,723, 13/358,319, and 13/451,786, each of which is assigned ofrecord to the assignee of the present application and is incorporated inits entirety by reference herein.

A portion 32 of the rotor 16 is shown in FIGS. 2-4. The rotor portion 32includes a rotor can 34 that includes a radially projecting spoked base36. The base 36 preferably includes a central plate 38 and an annularelevated floor 40. The rotor can 34 further includes a circumferentiallyextending outer support wall 42 and a discontinuous, circumferentiallyextending inner support wall 44 comprising a plurality of substantiallyrectangular columns 46 that are preferably formed during the molding ofthe rotor can 34. Formation of the columns 46 will be discussed ingreater detail below.

Preferably, both of the support walls 42,44 project axially upwardlyfrom the floor 40, with the floor 40 and the support walls 42,44 thusdefining a channel 48, as best shown in FIG. 4. An annular top wall 50extends between the inner and outer support walls 42,44 to enclose thechannel 48, with the exception of a plurality of windows 52, each ofwhich is bounded by a pair of the columns 46, the floor 40, and the topwall 50.

In the illustrated first embodiment, the rotor can 34 further includes aplurality of arcuately spaced apart dividers 54 extending radiallyinwardly from the outer support wall 42, as well as a plurality ofaxially extending, arcuately spaced apart inner positioning pegs 56 anda plurality of axially extending, arcuately spaced apart outerpositioning pegs 58. Like the columns 46, the pegs 56,58 and thedividers 54 are preferably formed during the molding of the rotor can34, as will be discussed in greater detail below. However, as will alsobe discussed in more detail below, it is permissible according tocertain aspects of the present invention for the pegs to be discretefasteners formed independently from the rotor can.

In the first embodiment, the central plate 38 of the rotor can 34 alsopreferably includes a plurality of ventilation slots 60 and ventilationapertures 62. It is also preferable that a plurality of support ribs 64are formed as part of the central plate 38. In addition to functioningas structural supports, the ribs 64 may also be configured in such amanner as to provide cooling assistance for the motor 10 by disturbingnearby air.

The rotor can 34 of the first preferred embodiment preferably comprisesa plastic material such as polypropylene, although any one or more of avariety of other materials may be used without departing from the scopeof the present invention. For instance, as will be discussed in moredetail below, it is preferable according to some embodiments of thepresent invention that the can be formed of aluminum.

It is also permissible and in some instances preferred that the materialof the rotor can 34 include reinforcing fibers such as glass fibers,although use of other reinforcement techniques or use of no additionalreinforcement is within the scope of the present invention.

As best shown in FIGS. 4 and 5, the rotor 16 preferably includes aplurality of arcuately spaced apart, radially extending pole segments66. Furthermore, as best shown in FIGS. 4 and 6, the rotor 16 preferablyincludes a plurality of arcuately spaced apart, radially extendingpermanent magnets 68. As used herein, “spaced” or “spaced apart” withreference to the pole segments should be interpreted as meaning thatadjacent pole segments do not directly contact each other. Likewise,“spaced” or “spaced apart” with reference to the magnets should beinterpreted as meaning that adjacent magnets do not directly contacteach other. The spacing of the pole segments and magnets will bediscussed in greater detail below.

The pole segments 66 and the magnets 68 are preferably alternatelyarranged in a circumferential direction. That is, a pole segment 66 islocated between each adjacent pair of magnets 68, and vice versa.Furthermore, the magnets 68 are preferably arranged such that adjacentmagnets present oppositely oriented polarities, with the poles beingoriented generally perpendicular to the radial direction. As shown inFIG. 6, for instance, the north pole N of a magnet 68 a is oriented toface the north pole N of a first adjacent magnet 68 b. The south pole Sof the magnet 68 a is oriented to face the south pole S of a secondadjacent magnet 68 c.

Preferably, the rotor can 34 of the first preferred embodiment isovermolded over and around the pole segments 66 and the magnets 68 so asto secure them in their appropriate positions. The dividers 54, thepositioning pegs 56 and 58, and the columns 46 therefore conform to thegeometry of the pole segments 66 and the magnets 68 when the moldedmaterial sets.

Preferably, as best shown in FIG. 1, the base 36 is configured forconnection of the rotor can 34 to a rotatable shaft 70. In the firstembodiment, the shaft 70 includes a machine connection end 72 and arotor connection end 74. The rotor connection end 74 is configured forengagement with a coupler 76. In the first preferred embodiment, suchengagement is effected by the interaction of the outer splines 78 on therotor connection end 74 and the inner splines 80 on the coupler 76. Thecoupler 76 also engages the base 36 of the rotor can 34, such that therotor can 34, the coupler 76, and the shaft 70 all rotate together abouta single axis of rotation. Although a single axis of rotation ispreferable, it is with the scope of the present invention for multipleaxes of rotation to be defined.

As shown in FIG. 4, engagement between the base 36 and the coupler 76 ispreferably by means of the preferred overmolding fabrication process.Although not shown, the outer surface of the coupler 76 is preferablysplined to enhance the connection. However, the base 36 and coupler 76may alternatively be interconnected, such as by a press fit or adhesiveconnection. Yet further, a variety of engagement means, whetherimplemented between the coupler 76 and the shaft 70 or between thecoupler 76 and the rotor can 34, are acceptable. For instance,interference screws, press fits, or adhesives could all be used, eithersingly or in combination.

Turning again to FIGS. 4 and 5, each pole segment 66 of the rotor 16preferably comprises steel or any one or more of a variety ofmagnetically conductive materials. Furthermore, each pole segment 66preferably includes a radially innermost section 82 and a radiallyoutermost section 84, with the sections 82,84 collectively presentingaxially spaced apart upper and lower faces 86 and 88, respectively. Theradially innermost section 82 preferably extends substantially arcuatelyrelative to the radially outermost section 84 and presents a radiallyinnermost face 90, a pair of side edges 92 and 94, and a discontinuousintermediate face 96. The radially outermost section 84 extendssubstantially radially outwardly from the intermediate face 96 andpreferably presents a pair of side faces 98 and 100 that intersect aradially outermost face 102 at respective corners 104 and 106. Thus, apair or shelves 107 are formed by the radially innermost section 82adjacent the side faces 98 and 100.

Preferably, each radially outermost section 84 is generally trapezoidalin shape, although any one or more of a variety of shapes arepermissible. It is also permissible according to some aspects of thepresent invention for the radially outermost sections 84 to beidentically configured or to vary from one another.

In the illustrated first embodiment, the edges 92,94 and corners 104,106are chamfered or rounded. However, it is within the scope of the presentinvention for sharp or otherwise configured edges and corners to beformed. Furthermore, for reasons including but not limited to thereduction of cogging torques, it is also within the scope of the presentinvention for a variety of shape modifications to be applied to the polesegments 66.

As best shown in FIG. 5, the pole segments 66 are preferably evenlyspaced from each other along an arcuate path. A spacing distance 108 isdefined between the adjacent side faces 98,100 of each adjacent pair ofradially outermost sections 82; and a spacing dimension 110 is definedbetween adjacent side edges 92,94 of each adjacent pair of radiallyinnermost sections 82. The spacing distance 108 is preferably greaterthan the spacing dimension 110.

Furthermore, it is preferable according to the first preferredembodiment of the present invention that the width (in a substantiallyarcuate direction) of each pole segment 66 is, at all radial positions,greater than both the spacing distance 108 and the spacing dimension110. However, it is permissible according some aspects of the presentinvention for the pole segment 66 to have a width that is smaller thanone or both of the spacing distance 108 and the spacing dimension 110.

In addition to the above features, it also is preferred that each polesegment 66 includes an inner positioning hole or opening 112 and anouter positioning hole or opening 114. As best shown in FIG. 4, eachpositioning hole 112,114 corresponds with one of the inner or outerpositioning pegs 56,58, respectively, with the pegs 56,58 being formedwithin the corresponding positioning holes 112,114 by inflow of therotor can material during the molding process of the rotor can 34. Suchformation of the pegs 56,58 within corresponding positioning holes112,114 ensures that both radial and circumferential movements of theassociated pole segments 66 are restricted.

Preferably, each pole segment 66 includes a first generally arcuatelyextending wall structure 112 a positioned radially outside of and inpart defining the inner positioning hole 112. Furthermore, each polesegment 66 preferably includes a second generally arcuately extendingwall structure 114 a positioned radially outside of and in part definingthe outer positioning hole 114. As best illustrated in FIG. 7, thesecond wall structure 114 a may also in part define the outerpositioning hole 112.

Preferably each of the wall structures 112 a, 114 a extendscontinuously, such that the positioning holes 112, 114 are closed andspaced both from each other and from the corresponding radiallyoutermost face 102. However, as will be discussed in greater detailbelow, it is permissible according to some aspects of the presentinvention for one or more discontinuous wall structures to be providedsuch that multiple positioning holes are interconnected and/or one ormore positioning holes intersect the radially outmost face and/or theradially innermost face so as to be non-enclosed.

Although the positioning holes 112,114 and, in turn, the positioningpegs 56,58 may suitably have an axially constant circularcross-sectional shape and size (the cross-section being taken transverseto the longitudinal axis of the respective peg), as illustrated, it iswithin the scope of the present invention for the holes 112,114 to be ofany suitable cross-sectional shape or to present an axially varyingcross-sectional shape or size. For instance, the positioning holes couldbe configured as rectangular prisms or be oval in cross-section; theycould be triangular in cross-section at the upper face 86 and circularin cross-section at the lower face 88; or they could be large incircular cross-sectional diameter at the upper face 86 and small at thelower face 88 such that an inverted conical space is defined.Furthermore, the holes might be generally trapezoidal in shape inkeeping with the shape of the radially outermost sections 84.

It is also acceptable for the positioning holes 112 to have a differentcross-sectional shape and/or size than the positioning holes 114 and/orfor the cross-sectional shape and/or size to vary among the positioningholes 112 and/or among the positioning holes 114. All of the positioningholes 112 could be circular in cross-section, for instance, while all ofthe positioning holes 114 could be square in cross-section.Alternatively, the positioning holes 112 and/or the positioning holes114 could alternate between circular and rectangular cross-sections fromone pole segment to the next.

Furthermore, although each pole segment 66 is shown having a pair ofpositioning holes 112,114 formed therethrough, it is within the scope ofthe present invention for one or more of the pole segments to include asingle positioning hole or more than two positioning holes. Evenfurther, positioning holes may be excluded entirely from some or all ofthe pole segments. For instance, first and second adjacent pole segmentscould present one and two positioning holes, respectively. As will bediscussed in greater detail below, if only a single positioning hole isprovided in a given pole segment, it is preferable that the hole bepositioned nearer to the radially outermost face than to the radiallyinnermost face.

As also illustrated in FIG. 4 and others, the windows 52 formed in theinner support wall 44 during the molding process allow the radiallyinnermost face 90 of each pole segment 66 to be exposed after completionof the rotor can 34 molding process, with the columns 46 and theradially innermost faces 90 preferably forming an at least substantiallycontinuous inner circumferential surface 116. The gap 20 (see FIG. 1) isdefined between the stator 18 and the inner circumferential surface 116.

Although the positioning pegs 56,58 restrict movement of the polesegments 66 in the manner described above, it is preferred that the polesegments 66 be additionally restricted against radial movement by theouter support wall 42; against circumferential movement by the adjacentdividers 54, wherein the dividers 54 are formed by inflow of the rotorcan material into the original spaces between the magnets 68 and thechamfered corners 104,106 of the pole segments 66; and against bothradial and circumferential movement by the columns 46. With furtherregard to the latter, it is preferred that an axially extending groove118 is formed in each circumferential side of a given support column 46in order to receive and wrap around the side edges 92,94 of the adjacentradially innermost section 82 to partially overlie the intermediate face96 and the radially innermost face 90 of the respective radiallyinnermost section 82.

Turning to FIGS. 4 and 6, each magnet 68 is preferably shaped as arectangular prism or block so as to present an inner face 120; an outerface 122; an upper face 124; a lower face 126; and side faces 128 and130, respectively. However, deviations from the illustrated shape may bemade without departing from the spirit of the present invention.

As shown in FIG. 4, each magnet 68 is positioned within a slot 132cooperatively defined by adjacent pairs of pole segments 66 (and, moreparticularly, the side and intermediate faces 96, 98, and 100); thecorresponding pair of dividers 54; and the outer and inner support walls42 and 44, respectively.

As best shown in FIG. 6, the magnets 68 are preferably evenly spacedfrom each other along an arcuate path. A maximum magnet spacing distance134 is defined between adjacent side faces 128,130 near the outer faces122 of adjacent magnets 68. A minimum magnet spacing distance 136 isdefined between adjacent side faces 128,130 near the inner faces 120 ofadjacent magnets 68. Furthermore, it is preferable that the width 138(in a substantially circumferential direction) of each magnet 68 besmaller than both the maximum magnet spacing distance 134 and theminimum magnet spacing distance 136. Also, as most clearly illustratedin FIG. 7, the width 138 of each magnet 68 is at least substantiallyequal to the maximum spacing distance 108, such that each magnet 68 iswider than the spacing dimension 110 and abuts or nearly abuts theradially adjacent shelves 97 (and intermediate faces 96). Preferably,the sizing of the pole segments 66 and the magnets 68 is such that gapstherebetween are minimized. Such gaps will likely exist due tomanufacturing limitations, however. The gaps may be air filled or filledwith plastic or another material without departing from the scope of thepresent invention. Gaps may also be intentionally provided withoutdeparting from the scope of the present invention, although such anarrangement is not as desirable as a gapless (or nearly gapless)arrangement.

Although the above dimensional relationships are preferred in accordancewith the first preferred embodiment of the present invention, variationsfrom such relationships are permissible without departing from the scopeof the present invention. The magnets might be unevenly spaced forinstance, be of varying widths, or be sized in such a manner as todefine distinct gaps relative to the adjacent pole segments.

Each of the magnets 68 is preferably a grade six (6) ferrite, neodymium,or ceramic magnet. The magnets are preferably each of the samecomposition and grade, although variation between magnets is permissiblewithout departing from the scope of the present invention. It is alsopossible that more than one of the above-named materials or multiplegrades of one or more of the above-named materials might be contained inthe same magnet. Use of other magnetic materials and/or grades is alsowithin the ambit of the present invention.

Although charging of the magnets 68 may be accomplished at any timedeemed convenient, provision of a plastic or otherwise non-magneticallyconductive rotor can 34 enables charging or re-charging of the magnets68 after completion of the molding of the rotor can 34 or, even further,after the rotor 16 is assembled in its entirety.

Preferably, the number of pole segments 66 is equivalent to the numberof permanent magnets 68, with that number being further equivalent tothe number of poles of the motor 10. In the illustrated firstembodiment, for instance, forty-two (42) pole segments 66 and forty-two(42) permanent magnets 68 are provided.

Although it is preferable for the rotor can 34 to be formed via anovermolding process by which the rotor can 34 encompasses the polesegments 66 and the magnets 68, it is within the scope of the presentinvention for the rotor can to be formed in more than one part and/or tobe formed prior to insertion of the pole segments 66 and magnets 68. Forinstance, the entire rotor can except for the top wall could be oneintegrally molded piece, with the pole segments 66 and the magnets 68being put into place relative to pre-formed pegs, dividers, columns, andwindows. The top wall could then be adhered or otherwise secured intoplace.

In a similar variation, a pre-formed rotor can could be provided inwhich the pegs are not integral with the can but instead are discreteand connected to the floor of the can via a press fit, adhesives,interengaging threads, or any of a variety of connection means known inthe art. One such variation will be discussed in greater detail below.

It will be appreciated that the inventive spoked rotor design describedherein is particularly effective in focusing or concentrating themagnetic flux. More specifically, for a given one of the magnets 68, theflux travels in at least substantially circumferentially oppositedirections into each of the adjacent pole segments 66. The pole segments66 then serve to redirect the flux in a radially inward direction.

Although it is feasible for the motor to be operable even if adjacentpole segments are in contact with each other, such contact would lead to“shorting” of the magnetic circuit. As a result, the flux would not beas focused. Furthermore, although it is feasible for the motor to beoperable with the magnet polarities varying to some extent from theoppositely oriented adjacent magnets described above, such anarrangement is not believed to be as desirable.

The motor 10 described above with reference to the first preferredembodiment provides numerous advantages. In a conventional outer rotormotor, for instance, high flux density is typically achieved usinghigher grade magnets (e.g., grade 9 ferrite magnets) and copper wiring.To achieve similar performance using less expensive lower grade magnetsand/or less expensive aluminum wiring typically requires increased stackheight. In some cases, however, the allowable stack increase will belimited based on the motor envelope available for the particularmachine. The flux density is thus limited based on axial spaceconstraints. In the inventive motor, however, the outer rotor spokedesign achieves higher flux density with lower grade magnets (e.g.,grade six (6) ferrite magnets) and aluminum wiring without any stackincreases, while still achieving performance comparable to that of amore expensive conventional design. Furthermore, although the inventivedesign preferably results in a larger outer diameter of the rotor, suchdiametrical expansion is typically more easily accommodated in themachine design than is axial expansion.

Another advantage is provided with regard to achieving both good lowspeed performance and good high speed performance. In particular, whileuse of a stack increase to achieve suitable flux density when usingaluminum wiring typically achieves acceptable low speed performance,high speed performance can be degraded. To compensate, stator redesignshave been implemented to reduce the number of poles and, in turn, toreduce the frequency and high speed losses. However, such an involvedapproach is less than ideal. In contrast, the present invention achievesgood performance at both low and high speeds without requiring statorredesign. This is particularly advantageous in washing machineapplications, wherein a low speed and high torque are required atstart-up and during at least part of the washing phase, and a high speedis required at spin.

Yet another advantage provided by the above-described design isincreased inductance without increased turns of the wiring, due to thepresence of the pole segments 66. Such increased inductance enables ahigher advance angle at high speed and, in turn, enables improved motorefficiency. This also allows for a higher number of poles to be used,resulting in improved demagnetization capability and improved lowerspeed performance.

Even further, improved sound characteristics may be provided by a motorconfigured in the manner described above.

Turning now to FIGS. 8-11, a second preferred embodiment is illustrated.It is initially noted that, with certain exceptions to be discussed indetail below, many of the elements of the rotor portion 210 of thesecond embodiment are the same as or very similar to those described indetail above in relation to the rotor portion 32 of the firstembodiment. Therefore, for the sake of brevity and clarity, redundantdescriptions and numbering will be generally avoided here. Unlessotherwise specified, the detailed descriptions of the elements presentedabove with respect to the first embodiment should therefore beunderstood to apply to the second embodiment, as well. Furthermore, itshould be understood that the rotor portion 210 of the secondillustrated embodiment could suitably be placed in an environmentsimilar to that shown in FIG. 1 or any of the other alternativeenvironments (e.g., electric scooters, etc.) previously described.

As shown in FIGS. 8 and 9, a rotor portion 210 is provided that includesa rotor can 212 including a radially projecting base 214. The base 214preferably includes a central plate 216 and, as best shown in FIG. 10,an annular elevated floor 218. The rotor can 212 further includes acircumferentially extending outer support wall 220 projecting axiallyupwardly from the floor 218. In the illustrated second embodiment, thecentral plate 216 includes a plurality of radially extending ventilationslots 222. Furthermore, the floor 218 preferably includes a plurality ofarcuately spaced inner fastener-receiving holes 224 and a plurality ofarcuately spaced outer fastener-receiving holes 226, with both sets ofholes 224,226 extending through the floor 218. Preferably, the inner andouter fastener-receiving holes 224,226 are threaded, althoughnon-threaded holes are allowable within the scope of the presentinvention.

The rotor can 212 of the second preferred embodiment preferablycomprises aluminum, although any one or more of a variety of materialsmay be used.

As shown in FIGS. 8-10, the second illustrated embodiment includes acoupler 228 for connection of the rotor can 212 to a rotor shaft (notshown). The coupler 228 of the second illustrated embodiment is securedthrough use of a press fit augmented with an interference screw 230.

Preferably, the pole segments 232 of the second illustrated embodimentare configured in the same manner as the pole segments 66 of the firstillustrated and include inner and outer positioning holes 234 and 236,respectively. Similarly, the magnets 238 of the second illustratedembodiment are preferably configured in the same manner as the magnets68 of the first illustrated embodiment. However, it is to be understoodthat any potential variants in pole segment or magnet constructiondescribed or implied above in relation to the pole segments 66 ormagnets 68 of the first embodiment apply likewise to the pole segments232 and/or magnets 238 of the second embodiment.

In contrast to the overmolding and resultant formation of positioningstructures such as pegs 56,58 and dividers 54 described in relation tothe first embodiment, the pole segments 232 of the second illustratedembodiment are preferably secured in the rotor can 212 by a plurality ofdiscrete inner and outer fasteners 240 and 242, respectively, thatcorrespond both to the inner and outer positioning holes 234,236 and tothe inner and outer fastener-receiving holes 224,226. Preferably, eachof the fasteners 240,242 is threaded so as to interengage with thethreads (not shown) of the fastener-receiving holes 224,226.Furthermore, each fastener 240 or 242 preferably presents an end 244 or246, respectively, that is substantially flush with the rotor can 212when the fasteners 240,242 are in place. However, the fasteners 240,242may be of a variety of lengths and may be partially threaded ornon-threaded. Furthermore, securement of the fasteners 240,242 in thefastener-receiving holes 224,226 can be through any means known in theart, including but not limited to use of adhesives, epoxies, or nuts. Itis also within the scope of the present invention for the inner andouter positioning holes 234,235 to be threaded.

Although the fasteners 240,242 are shown having a circularcross-sectional shape, it is within the scope of the present inventionfor the fasteners 240,242 to be of any suitable cross-sectional shapeand size or to present an axially varying cross-sectional shape or sizein conformance with any variations in the cross-sectional shape and/orsize of the positioning holes 234,236. Several potential variations havebeen discussed above with regard to the positioning holes 112,114 andpositioning pegs 56,58 of the first embodiment. The previously discussedvariations are to be understood as being generally applicable to thesecond embodiment, as well, with the fasteners 240,242 being analogousto the positioning pegs 56,58, respectively.

Furthermore, as discussed previously with respect to the firstembodiment, it is to be understood that one or more of the pole segmentsmay include a single positioning hole or more than two positioningholes. Even further, according to some aspects of the present invention,positioning holes may be excluded entirely from some of the polesegments. Preferably, the number of and location of the fasteners240,242 will correspond to the number of and location of the positioningholes.

It is also within the scope of the present invention for the shapes,sizes, and positions of the fastener-receiving holes 224,226 to varyfrom those shown in the illustrated second embodiment in order toreceive alternatively configured or arranged fasteners 240,242.

With continued regard to the fasteners 240,242, each fastener 240,242preferably includes a head 248,250, respectively, having at least onedimension larger than the largest cross-sectional dimension of theassociated positioning hole 234,236. Such sizing will ensure acontrolled depth of extension of the fasteners 240,242 into thepositioning holes 234,236 and the fastener-receiving holes 224,226.

Although the pole segments 232 are preferably secured to the rotor can212 by the fasteners 240,242, other securement means, including but notlimited to press fits, adhesives, or alternatively configured fasteners,fall within the scope of the present invention. For instance, discretefasteners might be provided that connect directly to the can via clips,adhesives, or other means rather than being threadably or otherwiseinserted into fastener-receiving holes formed in the can.

Furthermore, the magnets 238 may be secured to the rotor can 212 andbetween the pole segments 232 by any suitable means, including but notlimited to press fits (as shown), adhesives, or fasteners.

The advantages conferred by the second illustrated embodiment are atleast substantially similar to those described above with regard to thefirst preferred embodiment and therefore will not be discussedseparately herein.

A third preferred embodiment is illustrated in FIG. 12. It is initiallynoted that, with certain exceptions to be discussed in detail below,many of the elements of the rotor portion 310 of the third embodimentare the same as or very similar to those described in detail above inrelation to the rotor portion 32 of the first embodiment. Therefore, forthe sake of brevity and clarity, redundant descriptions and numberingwill be generally avoided here. Unless otherwise specified, the detaileddescriptions of the elements presented above with respect to the firstembodiment should therefore be understood to apply to the thirdembodiment, as well. Furthermore, it should be understood that the rotorportion 310 of the third illustrated embodiment could suitably be placedin an environment similar to that shown in FIG. 1 or any of the otheralternative environments (e.g., electric scooters, etc.) previouslydescribed.

As shown in FIG. 12, a rotor portion 310 is provided that includes arotor can 312 supporting pole segments 314 and magnets 316. Each of thepole segments 314 preferably includes a radially innermost portion 318and a radially outermost portion 320.

A positioning hole 322 is preferably formed in each of the radiallyoutermost portions 320. The pole segments 314 each preferably includegenerally arcuately extending wall structure 324 positioned radiallyoutside of and in part defining the corresponding positioning hole 322.

Preferably, the wall structure 324 presents a generally radial open slot326, with corresponding ones of the slots 326 and the positioning holes322 being interconnected.

As shown in FIG. 12, each of the positioning holes 322 preferablypresents a maximum positioning hole dimension in a generally arcuatedirection, while each of the slots 326 presents a constant slotdimension in a corresponding generally arcuate direction. Preferably,the maximum positioning hole dimensions are greater than thecorresponding slot dimensions, with corresponding ones of the slots andpositioning holes cooperatively forming keyholes 328 in the polesegments 314. Such relative dimensions preferably aid in preventingradially inward shifting of the pole segments 314.

It is permissible according to some aspects of the present invention,however, for the slot and maximum positioning hole dimensions to varyfrom those described above. For instance, each slot might presentdimensions that vary with radial position, and one or more of these slotdimensions might be larger than the corresponding opening dimension. Forinstance, the slot might be configured as a portion of a triangle. Insuch a configuration, the base might be positioned radially outwardlyfrom the positioning hole and have a dimension greater than the maximumpositioning hole dimension, while the regions of the slot defined by theupper portion of the triangle and positioned nearer or even adjacent thepositioning hole might have dimensions smaller than the maximumpositioning hole dimension. Radially inward shifting is thus restricted.

Ultimately, although any of a variety of dimensional relationshipsbetween the slots and the positioning holes are permissible within thescope of some aspects of the present invention, it is preferred that atleast the minimum generally arcuate dimension of each slot is smallerthan the corresponding maximum positioning hole dimension.

Among other things, provision of the slots 326 in addition to thepositioning holes 322 enables a decrease in the weight of each polesegment 314 and, in turn, a decrease in the overall weight of the rotorportion 310 and motor as a whole.

Each of the radially innermost portions 318 preferably presents aradially innermost face 330, while each of the radially outermostportions preferably presents a radially outermost face 332. Each of theslots 326 preferably extends to the radially outermost face 332.Furthermore, it is preferable that each of the positioning holes 322 ispositioned nearer to the radially outermost face than to the radiallyinnermost face. Such slot and positioning hole positioning preferablyenables a decreased impact on the flow of magnetic flux through eachpole segment 314.

Preferably, the rotor can 312 is overmolded, with the rotor can materialflowing into the keyholes 328 during the overmolding process to formpositioning pegs 334 that are integral with the can 312. It is noted,however, that it is permissible within the scope of some aspects of thepresent invention for a non-overmolded can and discrete fasteners to beprovided in conjunction with pole pieces defining keyholes therethrough.In such a case, the detailed descriptions of the elements presentedabove with respect to certain aspects of the second embodiment should beunderstood to apply to the third embodiment, as well.

The preferred forms of the invention described above are to be used asillustration only and should not be utilized in a limiting sense ininterpreting the scope of the present invention. Obvious modificationsto the exemplary embodiments, as hereinabove set forth, could be readilymade by those skilled in the art without departing from the spirit ofthe present invention.

The inventor hereby states his intent to rely on the Doctrine ofEquivalents to determine and assess the reasonably fair scope of thepresent invention.

What is claimed is:
 1. An electric motor comprising: a stator; and arotor rotatable about an axis and spaced at least in part radiallyoutside the stator, said rotor including— a plurality of arcuatelyspaced apart pole segments, each of said pole segments defining anopening therethrough and including a generally arcuately extending wallstructure positioned radially outside of and at least in part definingthe opening, a plurality of arcuately spaced apart magnets alternatelyarranged with the pole segments such that each of the pole segments ispositioned between an adjacent pair of the magnets, a rotor can at leastin part supporting the pole segments and the magnets, and a plurality ofpegs each extending through a corresponding one of the openings tosecure a corresponding one of the pole segments relative to the can. 2.The electric motor of claim 1, each of said wall structures presenting agenerally radial open slot, corresponding ones of said slots and saidopenings being interconnected.
 3. The electric motor of claim 2, each ofsaid slots presenting a minimum slot dimension in a generally arcuatedirection, each of said openings having at least a portion thereof thatis larger in the generally arcuate direction than the minimum slotdimension, said slot and said opening cooperatively forming a keyhole.4. The electric motor of claim 2, each of said pole segments presentinga radially outermost face, each of said slots extending to acorresponding one of the radially outermost faces.
 5. The electric motorof claim 4, each of said pegs being integrally formed with the can. 6.The electric motor of claim 5, said rotor can and pegs comprisingplastic overmolded over and around the pole segments and the magnets. 7.The electric motor of claim 6, said plastic comprising polypropylene. 8.The electric motor of claim 1, each of said pole segments presenting aradially outermost face, each of said wall structures extendingcontinuously so that the opening is closed and spaced from the radiallyoutermost face.
 9. The electric motor of claim 1, each of said pegsbeing a discrete fastener secured to the can.
 10. The electric motor ofclaim 1, said rotor can comprising aluminum.
 11. The electric motor ofclaim 1, each of said openings presenting a transverse cross-sectionhaving a shape and size that are at least substantially constant in anaxial direction.
 12. The electric motor of claim 1, said openings beinguniform.
 13. The electric motor of claim 1, each of said pole segmentsfurther defining a second opening therethrough, said second openingbeing radially spaced from the first opening.
 14. The electric motor ofclaim 1, said magnets comprising ferrite and/or neodymium.
 15. Theelectric motor of claim 1, adjacent ones of said magnets presentingoppositely oriented polarities.
 16. The electric motor of claim 15, eachof said polarities being oriented generally perpendicular to anassociated radial direction.
 17. The electric motor of claim 1, each ofsaid pole segments comprising a magnetically conductive material. 18.The electric motor of claim 17, each of said pole segments comprisingsteel.
 19. The electric motor of claim 1, each of said pole segmentspresenting a radially innermost face and a radially outermost face, eachof said openings being positioned closer to the corresponding outermostface.
 20. The electric motor of claim 1, each of said pole segmentscomprising— a body including radially outermost and innermost sections,said outermost section presenting a pair of spaced apart side faces,said innermost section projecting arcuately relative to each of the sidefaces to form a pair of spaced apart shelves.
 21. The electric motor ofclaim 20, each of said bodies being trapezoidal in shape.
 22. Theelectric motor of claim 20, said pole segments being at leastsubstantially evenly spaced apart along an arcuate path, said polesegments defining a spacing distance between adjacent ones of the sidefaces of each adjacent pair of bodies, each of said shelves presentingan outermost side edge spaced from a corresponding one of the sidefaces, said pole segments defining a spacing dimension between adjacentones of the side edges of each adjacent pair of shelves, said spacingdimension being less than said spacing distance.
 23. The electric motorof claim 22, each of said magnets presenting a magnet width in an atleast substantially arcuate direction that is at least substantiallyequal to the spacing distance.
 24. The electric motor of claim 23, eachof said magnets radially abutting one of the shelves of each adjacentone of the pole segments.